When we first met Don Draper, back in 2007, which is to say, back in 1960, he was like a billboard for his own charisma. Handsome as a racecar, he clearly got a kick out of his own cinematic virility, using it to manipulate both men and women. Yet Don spent that day in a panic, struggling to devise an ad for Lucky Strike cigarettes. “I have nothing,” he kvetched to his mistress. “I am over. And they’re finally gonna know it. Next time you see me, there’ll be a bunch of young executives picking meat off my ribs.”

His nerves were a kind of theatre, of course. Twenty-three minutes later, in the Sterling Cooper boardroom, Don pulled a perfect pitch out of thin air, the first of many resurrections. His colleague Pete wanted Lucky Strike to embrace death, but Don knew that a distraction was needed. “Everybody else’s tobacco is poisonous,” he explained to the client. “Lucky Strike’s is toasted.” As cable television’s latest bad boy, with all the sex and none of the violence of his predecessors, Draper was an immediate hit with audiences: the man who could read symbols but couldn’t be read himself—a mystery wrapped in an enigma wrapped in Jon Hamm.

In its sixth season, “Mad Men” is in certain ways an even more ambitious show than it was at the start, with an idiosyncratic, legitimately perverse sense of character and plot. (What other show would have someone run over a British interloper’s foot with a lawnmower, or include a blackface performance? Hey, remember when Duck forced his dog out the front door? The series doesn’t get enough credit for its sick sense of humor.) It began at a slow pace, and, as seasons passed, it had the confidence to get even slower, establishing a bold TV aesthetic: hypnotic, with a defiant staginess, as dense with textual significance as “Lost.” If there’s wallpaper to be ripped off the wall, suggesting a crack in society’s civilized veneer, well, then, an innocent little boy is going to rip it. “Mad Men” is brocaded with ultra-Freudian imagery—a gold violin, a rotten tooth—and it uses its camera less as a pair of eyes than as a proscenium, framing images as if they were posters. (You can see the influence of the show’s rhythms all over TV these days, on dramas like Sundance’s “Top of the Lake” and “Rectify,” as well as on HBO’s “Enlightened” and BBC’s “The Hour.”) While some of the showrunner Matt Weiner’s scenes are clunky—do we really need to see Peggy imagining herself kissing Ted Chaough?—more often they linger in the imagination, slurring and turning surreal, much as actual memories do. Having spanned so many years, both imaginary and real, “Mad Men” has become a show that induces nostalgia for itself.

Yet, if “Mad Men” ’s style is still influential, its substance is a different matter. And the trouble, oddly, is Don. This season began with a wonderfully candied, elliptical episode, two hours long. The show’s Kodak time machine has spun to December, 1967, and Don is on a luxurious Hawaiian vacation, paid for by a client. In this artificial paradise, he has stoned sex with Megan, his lovely second wife, gazes at a faux luau, and relaxes on the beach while reading Dante’s Inferno: “Midway in our life’s journey, I went astray from the straight road, and woke to find myself alone in a dark wood.” Then he returns to Manhattan, to a life that seems stable and real, until the final sequence, which nimbly inverts “Mad Men” ’s pilot: instead of a wife being revealed, out pops a hidden mistress. That would be the woman who gave Don his Dante—Sylvia Rosen, his latest dimpled brunette, the wife of a close friend, a crucifix dangling from her guilty clavicle.

Like the show’s pilot, the episode was stocked with intimations of death: a doorman has a heart attack; there’s a funeral for Roger’s mother; at one point, Megan runs her hand over Don’s face, closing his eyes as if he were in a coffin. But Don has lost control of his brand. Now in his forties, an established partner at a firm that bears his name, he pitches an ad that falls flat, precisely because he is unable to conceal what’s on his mind. It’s a pencil sketch of footprints on a beach, a man’s suit lying on the sand, and an empty ocean vista. Everyone else at the meeting sees it for what it is: a fantasy of suicide. His code broken, Don falters, unable to improvise in front of the people he used to dominate. When he attends Roger’s mother’s funeral, he vomits publicly. “He was just saying what everyone else was thinking,” Roger says.

This is a fantastic theme, in theory—the downfall of the man in the suit, as foretold by the show’s iconic opening credits. The episode was beautifully structured, but it was also worrisome: Don had become a drag. “Mad Men” ’s other characters—Peggy, Roger, Pete, Joan, the bizarre Betty (her blond hair now dyed Veronica black)—largely feel like individuals, escapees from their archetypes. Newer roles, including Don’s black secretary, Dawn, are more contrived, but the show keeps finding fresh angles on complicated subjects, like the death of Martin Luther King, Jr., which it re-created as a tone poem of white-person awkwardness. But Don, instead of being the show’s engine, has become its anchor—heavy, even in the sixties sense. This is true despite the excellent performance of Hamm, who remains the most watchable man on earth, even when he’s doing nothing but glaring over a tumbler of Scotch. (Don began the show mocking beatniks, and lately he’s been sneering at swingers. I wouldn’t be surprised if he curls his lip when he has an orgasm.)

As the island was to “Lost,” Don Draper is to “Mad Men.” He was a great premise, a mystery we were dying to understand. But, the more the puzzle has been filled in, the more he’s begun to feel suspiciously like a symbol, a thesis title rather than a character: “Appearance Versus Reality”; “American Masculinity as Performance”; “The Links Between Prostitution, Marriage, and the Ad Game.” I’d hoped that the death of Don’s California-stoner muse, Anna, two seasons ago—in one of the series’ standout episodes, “The Suitcase”—would work as an exorcism, but instead Weiner doubled down, adding fresh flashbacks, to the point that even JT LeRoy might think that he was laying it on a bit thick.

To recap: Don’s real name is Dick Whitman. His prostitute mother died in childbirth; his dad, her john, beat him. His fundamentalist stepmother called him a “whore’s child.” Then his father got kicked in the head by a horse, and the stepmother moved in with her sister, herself a prostitute, living in a brothel. The stepmother, heavily pregnant with Don’s half brother, prostituted herself to her brother-in-law, as the teen-age Don knelt outside her door. He watched them, through the keyhole, have sex. C’mon, now. This is no longer the backstory of a serial adulterer; it’s the backstory of a serial killer.

We haven’t even got to the part where Whitman goes to fight in Korea, accidentally blows up his superior officer, Don Draper, steals his identity, forms a secret relationship with his widow (she’s motherly, yet also somewhat prostitute-like, since he pays for her upkeep), becomes a greaser, and seduces a model who is also concerned primarily with appearances. Eventually, he gets into advertising, and when his half brother, Adam, finds him, Don rejects him, and Adam hangs himself. It’s not that none of this makes sense, or could make sense; it’s just too much, overdetermined. None of the other characters has this sort of reverse-engineered psychology, and for good reason: it’s a lazy way to impose meaning. Nested among better scenes, the flashbacks feel like a high-school production of “The Grapes of Wrath.” (Back in Season 1, when Don was canoodling with the department-store heiress Rachel Menken and reading “Exodus,” I wondered if his dark secret was that his mother was a Jew. Life was so much simpler then!)

This isn’t a death knell for the show—American life may have no second acts, but TV series sure do. Talking to his shrink, Roger has a great monologue about doors and windows; it echoes Don’s quote from Dante but also suggests something about the series’ own laissez-faire notion of a character arc. “Look, life is supposed to be a path, and you go along, and these things happen to you, and they’re supposed to change you, change your direction, but it turns out that’s not true. Turns out the experiences are nothing. They’re just some pennies you pick up off the floor, stick in your pocket, and you’re just going in a straight line to you-know-where.” (The penny imagery was itself quickly picked up, in the keyhole flashback and then as a signal to Don from his mistress.)

It’s an interesting notion: life as an improvisation, a brainstorming session that won’t necessarily find the solution. That’s the part of “Mad Men” eager to explore new ideas about human personality. Then, there’s the other part, which, two episodes ago, seemed like an attempt to reignite that old fantasy Don Draper, the one the audience fell for, early on. In quick succession, he dropped a creepy client, fixed a new account, and solved a structural problem—for both the series and the firm—by suggesting a merger. The episode was a ton of fun, but it also felt a little cheap, as if we were getting what we wanted, instead of what we needed.

Then again, this déjà vu didn’t erase the idea of an unhappy ending. “I love you like this,” Megan purred, as Don struggled to brand a car with no name. “Desperate and scared?” he said. “Fearless,” she replied, saying that she’d do anything to help. Her closing line hinted at the finale that the show keeps flashing like a fan dancer: “Then you can jump from the balcony and fly to work. Like Superman.” ♦

His show suggested that TV could puncture the culture, rather than prop it up.

As the years passed, Tom grew more entrenched in his homelessness. He was absorbed in lofty fantasies and private missions, aware of the basest necessities and the most transcendent abstractions, and almost nothing in between.